A damper device is arranged at a power transmission path between an engine and a clutch, for example, so as to absorb a torque fluctuation generated between the engine and a transmission. When the torque fluctuation is generated, the damper device absorbs torsion (the torque fluctuation) by means of elastic force of coil springs and friction force (hysteresis torque) generated by friction materials. A conventional damper device includes two kinds of damper portions (coil springs and elastic members), each of which is arranged in series with each other, in order to absorb a torque fluctuation in accordance with a driving state of an engine (for example, at the time when the engine is started, and at the time when the engine is in an idling state).
According to JP2003-278836A, a torque fluctuation absorber absorbs a torque fluctuation of a driving source in a hybrid vehicle having both an internal combustion engine and an electric motor, which is driven by means of electricity supplied from a battery, as the driving source, and an electric generator, which is configured to charge the battery with an electrical energy generated by driving the internal combustion engine. The torque fluctuation absorber is configured to absorb the torque fluctuation of the internal combustion engine by means of a first torsion member and a second torsion member, whose torsional rigidity is larger than the first torsion member. The torsional rigidity of the first torsion member is set to absorb a torque fluctuation of the internal combustion engine, the torque fluctuation being generated when the electric generator generates the electrical energy by means of the internal combustion engine.
However, in the torque fluctuation absorber according to JP2003-278836A, the first torsion member, which is provided at a radially inward portion, is arranged between a flange portion and a hub portion. As a result of such structural limitation, the first torsion member of the torque fluctuation absorber is limited to absorb a small amount of torque. Accordingly, a performance of absorbing the torque fluctuation by means of the first torsion member is achieved only when the small amount of torque is generated from the engine that is in the idling state and the like. Further, a torsion angle may not be set to be large at a position where the first torsion member is arranged, and therefore, the torsional rigidity is set at a high level so as to absorb only a relatively small amount of torque.
Further, the first torsion member is arranged at a space between an inner spline of the flange portion and an outer spline of the hub portion in a circumferential direction. Therefore, only a part of end surfaces of the first torsion member contact the inner spline of the flange portion and the outer spline of the hub portion, and as a result, strength is limited and an impact is easily generated. Furthermore, splines are formed at the flange portion and the hub portion. Therefore, a processing cost is increased.
Furthermore, the hub portion, which is arranged at an output side, may include a large amount of inertia in order to absorb noise and vibration. However, according to the torque fluctuation absorber in JP2003-278836A, the hub portion is arranged at a more radially inward portion than the flange portion, and therefore, inertia of the hub portion may not be set to a large level.
A need thus exists for a damper device, which is not susceptible to the drawback mentioned above.